Lymphocytic Colitis With Ileal Extension Following Oyster Consumption: A Case Report.

Lymphocytic colitis is an uncommon cause of chronic, non-bloody diarrhea characterized histologically by increased intraepithelial lymphocytes within the colonic mucosa, typically with preserved architecture. We present a case of an 84-year-old Caucasian male patient with a history of hypertension, obstructive sleep apnea, benign prostatic hyperplasia, and essential tremor, who developed persistent watery diarrhea, profound fatigue, and unintentional weight loss of 22 pounds within several days after consuming fried oysters at a local restaurant. Initial evaluation at multiple facilities revealed hypotension, hypokalemia, and acute kidney injury, with negative infectious stool studies, unremarkable abdominal imaging, and no evidence of celiac disease. Despite supportive care and antimotility therapy, symptoms persisted, and the patient required repeat hospitalization. A computed tomography (CT) scan demonstrated colonic air-fluid levels consistent with a diarrheal state without inflammatory changes. Colonic biopsies revealed classic lymphocytic colitis, with rare extension into the terminal ileum. The patient experienced significant improvement after initiation of intravenous methylprednisolone, with resolution of vomiting, reduction in stool frequency, normalization of electrolytes, and improvement in renal function, sustained over several weeks of follow-up. This case highlights the diagnostic challenges of lymphocytic colitis, which may present with subacute symptoms that mimic irritable bowel syndrome or chronic infection. The temporal association with recent oyster consumption raises the possibility of a food antigen-mediated trigger, an uncommon but clinically relevant consideration in the pathogenesis of lymphocytic colitis.